249
Federal Aviation Administration, DOT
§ 25.479
displacement of the center of gravity is
maintained within these limits.
(c)
Landing gear dimension data. Fig-
ure 1 of appendix A contains the basic
landing gear dimension data.
[Amdt. 25–23, 35 FR 5673, Apr. 8, 1970, as
amended by Doc. No. FAA–2022–1355, Amdt.
25–148, 87 FR 75710, Dec. 9, 2022; 88 FR 2813,
Jan. 18, 2023]
§ 25.473
Landing load conditions and
assumptions.
(a) For the landing conditions speci-
fied in § 25.479 to § 25.485 the airplane is
assumed to contact the ground—
(1) In the attitudes defined in § 25.479
and § 25.481;
(2) With a limit descent velocity of 10
fps at the design landing weight (the
maximum weight for landing condi-
tions at maximum descent velocity);
and
(3) With a limit descent velocity of 6
fps at the design take-off weight (the
maximum weight for landing condi-
tions at a reduced descent velocity).
(4) The prescribed descent velocities
may be modified if it is shown that the
airplane has design features that make
it impossible to develop these veloci-
ties.
(b) Airplane lift, not exceeding air-
plane weight, may be assumed unless
the presence of systems or procedures
significantly affects the lift.
(c) The method of analysis of air-
plane and landing gear loads must take
into account at least the following ele-
ments:
(1) Landing gear dynamic character-
istics.
(2) Spin-up and springback.
(3) Rigid body response.
(4) Structural dynamic response of
the airframe, if significant.
(d) The landing gear dynamic charac-
teristics must be validated by tests as
defined in § 25.723(a).
(e) The coefficient of friction between
the tires and the ground may be estab-
lished by considering the effects of
skidding velocity and tire pressure.
However, this coefficient of friction
need not be more than 0.8.
[Amdt. 25–91, 62 FR 40705, July 29, 1997; Amdt.
25–91, 62 FR 45481, Aug. 27, 1997; Amdt. 25–103,
66 FR 27394, May 16, 2001]
§ 25.477
Landing gear arrangement.
Sections 25.479 through 25.485 apply
to airplanes with conventional ar-
rangements of main and nose gears, or
main and tail gears, when normal oper-
ating techniques are used.
§ 25.479
Level landing conditions.
(a) In the level attitude, the airplane
is assumed to contact the ground at
forward velocity components, ranging
from V
L1
to 1.25 V
L2
parallel to the
ground under the conditions prescribed
in § 25.473 with—
(1) V
L1
equal to V
S0
(TAS) at the ap-
propriate landing weight and in stand-
ard sea level conditions; and
(2) V
L2
equal to V
S0
(TAS) at the ap-
propriate landing weight and altitudes
in a hot day temperature of 41 degrees
F. above standard.
(3) The effects of increased contact
speed must be investigated if approval
of downwind landings exceeding 10
knots is requested.
(b) For the level landing attitude for
airplanes with tail wheels, the condi-
tions specified in this section must be
investigated with the airplane hori-
zontal reference line horizontal in ac-
cordance with Figure 2 of Appendix A
of this part.
(c) For the level landing attitude for
airplanes with nose wheels, shown in
Figure 2 of Appendix A of this part, the
conditions specified in this section
must be investigated assuming the fol-
lowing attitudes:
(1) An attitude in which the main
wheels are assumed to contact the
ground with the nose wheel just clear
of the ground; and
(2) If reasonably attainable at the
specified descent and forward veloci-
ties, an attitude in which the nose and
main wheels are assumed to contact
the ground simultaneously.
(d) In addition to the loading condi-
tions prescribed in paragraph (a) of this
section, but with maximum vertical
ground reactions calculated from para-
graph (a), the following apply:
(1) The landing gear and directly af-
fected attaching structure must be de-
signed for the maximum vertical
ground reaction combined with an aft
acting drag component of not less than
25% of this maximum vertical ground
reaction.
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250
14 CFR Ch. I (1–1–24 Edition)
§ 25.481
(2) The most severe combination of
loads that are likely to arise during a
lateral drift landing must be taken
into account. In absence of a more ra-
tional analysis of this condition, the
following must be investigated:
(i) A vertical load equal to 75% of the
maximum ground reaction of § 25.473
must be considered in combination
with a drag and side load of 40% and
25% respectively of that vertical load.
(ii) The shock absorber and tire de-
flections must be assumed to be 75% of
the deflection corresponding to the
maximum ground reaction of
§ 25.473(a)(2). This load case need not be
considered in combination with flat
tires.
(3) The combination of vertical and
drag components is considered to be
acting at the wheel axle centerline.
[Amdt. 25–91, 62 FR 40705, July 29, 1997; Amdt.
25–91, 62 FR 45481, Aug. 27, 1997]
§ 25.481
Tail-down landing conditions.
(a) In the tail-down attitude, the air-
plane is assumed to contact the ground
at forward velocity components, rang-
ing from V
L1
to V
L2
parallel to the
ground under the conditions prescribed
in § 25.473 with—
(1)
V
L1
equal to
V
S0
(TAS) at the ap-
propriate landing weight and in stand-
ard sea level conditions; and
(2)
V
L2
equal to
V
S0
(TAS) at the ap-
propriate landing weight and altitudes
in a hot day temperature of 41 degrees
F. above standard.
(3) The combination of vertical and
drag components considered to be act-
ing at the main wheel axle centerline.
(b) For the tail-down landing condi-
tion for airplanes with tail wheels, the
main and tail wheels are assumed to
contact the ground simultaneously, in
accordance with figure 3 of appendix A.
Ground reaction conditions on the tail
wheel are assumed to act—
(1) Vertically; and
(2) Up and aft through the axle at 45
degrees to the ground line.
(c) For the tail-down landing condi-
tion for airplanes with nose wheels, the
airplane is assumed to be at an atti-
tude corresponding to either the stall-
ing angle or the maximum angle allow-
ing clearance with the ground by each
part of the airplane other than the
main wheels, in accordance with figure
3 of appendix A, whichever is less.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–91, 62 FR 40705, July 29,
1997; Amdt. 25–94, 63 FR 8848, Feb. 23, 1998]
§ 25.483
One-gear landing conditions.
For the one-gear landing conditions,
the airplane is assumed to be in the
level attitude and to contact the
ground on one main landing gear, in
accordance with Figure 4 of Appendix
A of this part. In this attitude—
(a) The ground reactions must be the
same as those obtained on that side
under § 25.479(d)(1), and
(b) Each unbalanced external load
must be reacted by airplane inertia in
a rational or conservative manner.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–91, 62 FR 40705, July 29,
1997]
§ 25.485
Side load conditions.
In addition to § 25.479(d)(2) the fol-
lowing conditions must be considered:
(a) For the side load condition, the
airplane is assumed to be in the level
attitude with only the main wheels
contacting the ground, in accordance
with figure 5 of appendix A.
(b) Side loads of 0.8 of the vertical re-
action (on one side) acting inward and
0.6 of the vertical reaction (on the
other side) acting outward must be
combined with one-half of the max-
imum vertical ground reactions ob-
tained in the level landing conditions.
These loads are assumed to be applied
at the ground contact point and to be
resisted by the inertia of the airplane.
The drag loads may be assumed to be
zero.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–91, 62 FR 40705, July 29,
1997]
§ 25.487
Rebound landing condition.
(a) The landing gear and its sup-
porting structure must be investigated
for the loads occurring during rebound
of the airplane from the landing sur-
face.
(b) With the landing gear fully ex-
tended and not in contact with the
ground, a load factor of 20.0 must act
on the unsprung weights of the landing
gear. This load factor must act in the
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